In a radio communication system, uplink power control plays an important role; on one hand, UE is required to have enough transmit power to meet required Quality of Service (QoS), on the other hand, user interference in the system needs to be reduced to overcome the influence of path loss, fast fading and shadow fading of a radio environment on radio signal transmission; besides, energy consumption of UE needs to be saved as far as possible. Power control plays a very important role in performance improvement of the radio communication system.
Since different UEs in a cell of an LTE system use different time-frequency resources, user interference in the cell is relatively small. The uplink power control of the LTE system includes power control of a Physical Uplink Shared Channel (PUSCH), a Physical Uplink Control Channel (PUCCH), a Physical Random Access Channel (PRACH) and a Sounding Reference Symbol (SRS). The power control described below refers to the uplink power control.
Hybrid Automatic Repeat Request (HARQ) is one of error control techniques of which the purpose is to improve signal transmission quality and guarantee information reliability. The HARQ is an error correction method which combines an Automatic Repeat Request (ARQ) technique and a Forward Error Correction (FEC) technique, and is an implicit link adaptation technique based on a link layer. The FEC technique refers to that error correction is performed based on redundant information in received data; The ARQ technique guarantees signal quality based on a error code detection and a retransmission request; the HARQ of the LTE system is divided into adaptive retransmission and non-adaptive retransmission, and the difference between the adaptive retransmission and the non-adaptive retransmission is whether modulation and coding schemes (MCS) used for retransmission are the same and whether radio resources used for retransmission are the same.
In a protocol, there is a Transmit Power Control (TPC) adjustment item in a PUSCH power calculation formula; the TPC adjustment value belongs to a closed loop power adjustment and is a power adjustment value which is determined by an evolved Node B (eNB) according to a measured Signal To Interference Plus Noise Ratio (SINR) and a target SINR and other factors, and is fed back to UE through a Physical Downlink Control Channel (PDCCH).
The mode of power control can be divided into two modes, namely an accumulation mode and an absolute value mode. The accumulation mode is to adjust step by step based on previously accumulated power, while the absolute value mode is to adjust to a target value directly and is only effective for PUSCH data transmitted within a current Transmission Time Interval (TTI); compared with the accumulation mode, the absolute value mode can adjust the transmit power of UE more rapidly. The specific power control mode applied by UE is configured by a Radio Resources Control (RRC) layer. The TPC adjustment value can be transmitted to UE independently through Downlink Control Information (DCI) format 0 (referred to DCI0 for short) of a PDCCH, or can be transmitted to the UE through DCI format 3/3A (referred to DCI3/3A for short) after being jointly encoded with a TPC adjustment value of other UE; if DCI0 exists, the TPC adjustment value indicated by the DCI3/3A is not necessarily taken into account.
For new data transmission and PUSCH adaptive retransmission, an eNB certainly transmits DCI0 through a PDCCH, wherein a power value that UE needs to adjust (i.e., a TPC adjustment value) is accordingly included in the DCI0. While for non-adaptive retransmission, an eNB can transmit a power value that UE needs to adjust through DCI3/3A, however, the number of UEs contained in the DCI3/3A is limited, wherein the DCI3 can contain adjustment values of
  N  =      ⌊                  L                  format          ⁢                                          ⁢          0                    2        ⌋  UEs at most, the DCI3A can contain TPC adjustment values of Lformat 0 UEs at most, the Lformat 0 is the number of bits of DCI0 and correlates with an eNB scheduling algorithm; therefore, it can not be guaranteed that each UE obtains its own TPC adjustment value. At this moment, a high SINR might not be obtained for the eNB for correct decoding even after several times of retransmission carried out by UE, thus retransmission radio resources are wasted, a transmission delay is increased and a throughput rate of an LTE system is reduced.